Reconstructing matter profiles of spherically compensated cosmic regions in ΛCDM cosmology

Abstract

The absence of a physically motivated model for large scale profiles of cosmic voids limits our ability to extract valuable cosmological information from their study. In this paper, we address this problem by introducing the spherically compensated cosmic regions, named CoSpheres. Such cosmic regions are identified around local extrema in the density field and admit a unique compensation radius R 1 where the internal spherical mass is exactly compensated. Their origin is studied by extending the standard peak model and implementing the compensation condition. Since the compensation radius evolves as the Universe itself, R 1 (t) ∝ a(t), CoSpheres behave as bubble Universes with fixed comoving volume. Using the spherical collapse model, we reconstruct their profiles with a very high accuracy until z = 0 in N-body simulations. CoSpheres are symmetrically defined and reconstructed for both central maximum (seeding haloes and galaxies) and minimum (identified with cosmic voids). We show that the full non linear dynamics can be solved analytically around this particular compensation radius, providing useful predictions for cosmology. This formalism highlights original correlations between local extremum and their large scale cosmic environment. The statistical properties of these spherically compensated cosmic regions and the possibilities to constrain efficiently both cosmology and gravity will be investigated in companion papers.

Growth rate of spherical voids with non-comoving dark matter and baryons

“…In general, cosmic voids are approximately spherical structures that tend to become more spherical with time. This result is known as the 'bubble theorem' [37], also discussed in [31][32][33][34][38][39][40]. Leveraging spherical symmetry (or quasi-symmetry), void formation and evolution have also been examined in the context of general relativity, including the Lemaître-Tolman-Bondi (LTB) dust models [41][42][43][44] and the quasi-spherical Szekeres models [25][26][27]45].…”

Non-comoving baryons and cold dark matter in cosmic voids

“…These studies have put forward various forms of "universal" density profiles [48,49] that fit observations and catalogues. However, given the fact that cosmic voids are approximately spherical structures that tend to become more spherical as they evolve (see [50] for the first proof of this fact known as the "bubble theorem" 1 and also [4][5][6][7][51][52][53] for further discussions and comparison with Nbody simulations), it is also feasible to study them by means of spherically symmetric, exact and numerical solutions of Einstein's equations. As examples of analytic and semianalytic general relativistic studies, there are many based on Lemaître-Tolman-Bondi (LTB) dust models [54][55][56][57], or the more general non-spherical (but quasi-spherical) Szekeres models [58][59][60][61].…”

Modeling the environmental dependence of the growth rate of cosmic structure

“…These approximations, as well as the spherical evolution (e.g. [29] [30]) have been investigated in the literature and recently the authors of [28] have found that both Zeldovitch and spherical evolution lead to a similar evolution of an initially spherical density perturbation, which is in very good agreement with N-body simulations in some special cases (e.g. voids that are compensated, ∆(R = R v ) > 0, where R v is the radius of a void).…”

“…For instance using the well-known Zeldovitch approximation [27], which links the initial density profiles ∆(a ini ) to a later time ∆(a) assuming no shell-crossing and mass conservation (e.g. [28]). These approximations, as well as the spherical evolution (e.g.…”